1. Field of the Invention
This invention relates to an apparatus for obtaining rotational or linear driving energy from vibration energy, a so-called vibration drive motor, and in particular to a vibration drive motor utilizing the bending vibration of a bar-like vibration member in two directions.
2. Related Background Art
Most of the conventional motors utilize an electromagnetic force and they are comprised of iron cores, copper windings and permanent magnets and thus, require a great number of parts and accordingly a large size and increased weight of the motor.
To provide motors which eliminate these disadvantages, studies of a motors of new type utilizing ultrasonic wave vibration have been actively made in recent years. For example, as seen in Japanese Laid Open Patent Application No. 148682/1983, there is an apparatus in which a travelling vibration wave comprising a combined vertical wave and horizontal wave is generated in the surface of a vibration member and a moving member urged thereby is rotationally or linearly driven. This apparatus requires a small number of parts and is simple in construction, and thus leads to the provision of a relatively good motor. However, this apparatus, which uses a travelling vibration wave, unavoidably requires a circulating portion to be formed in the vibration member in order to cause the vibration wave to travel uninterruptedly, and is still insufficient to make the motor compact and light in weight. Further, according to this apparatus, a predetermined proportional relation is always kept between the amplitude of the vertical wave and the amplitude of the horizontal wave in principle and therefore, it is difficult to freely control the amplitude of the vertical wave which originally provides the drive force of the moving member and the amplitude of the horizontal wave which provides the supporting force of the moving member, and it is difficult to control the speed and drive force corresponding to a variation in the motor load.
There is also a vibration wave motor of the type as seen in Japanese Laid-Open Patent Application No. 62880/1985. This motor is basically such that a standing wave of vertical vibration is excited to thereby obtain a drive force. Now, generally, the wavelength of vertical vibration (vertical wave) has a value inherent to the material of the vibration member when the number of vibration is a predetermined value. The number of vibration of a vibration wave motor is usually of the order of 20-50 KHz to eliminate noise and from the limitations of vibration amplitude, etc. Accordingly, in the vibration wave motor of the above described type, assuming that the material of the vibration member is a metal material such as steel, the half wavelength is of the order of 60-150 mm and it is necessary that the vibration member itself have at least a length of this order. Further, the addition of structural parts for driving will result in considerable dimensions as a whole and thus, it becomes difficult to construct a compact vibration wave motor. Moreover, to revolve the vibration wave motor of this type in forward and reverse directions, a forward-reverse revolution device is necessary, and this also leads to structural complexity.